THE SPECIFIC GRAVITY OF THE SEA, ETC. 209 



;behind, is just sufficient to counterbalance, by its weight, the 

 efiect of thermal dilatation upon the specific gravity of sea water 

 between the parallels of 34° north and south. As we go from 

 34° to the equator, the water grows warm and expands. It would 

 become lighter, but the trade-winds, by taking up vapour without 

 -salt, make the water salter, and therefore heavier. The con- 

 clusion is, the proj^ortion of salt m sea water, its expansibihty be- 

 tween 62" and 82"" (for its thermal dilaiahility varies with its tem- 

 peratm^e), and the thirst of the trade-winds for vapour, are, where 

 they blow, so balanced as to produce perfect compensation ; and 

 4X more beautiful compensation cannot, it appears to me, be found 

 in the mechanism of the universe than that wdiich we have here 

 stiunbled upon. It is a triple adjustment : the power of the sun 

 to expand, the power of the winds to evaporate, and the quantity 

 of salts in the sea — these are so proportioned and adjusted that 

 when both the mnd and the sun have each played with its forces 

 upon the intertropical waters of the ocean, the residuum of heat and 

 of salt should be just such as to .balance each other in their efiects, 

 and so the aqueous equilibrium of the torrid zone is preserved. 



437. Nor are these the only adjustments efiected by this ex- 

 compensating in- quisito Combination of compensations. If aU the 

 ^^"""■■^*- intertropical heat of the sun were to pass into the 



seas upon which it falls, simply raising the temperature of theu^ 

 waters, it would create a thermo-dynamical force in the ocean 

 capable of transporting water scalding hot from the torrid zone, 

 and spreading it, while still in the tepid state, around the poles. 

 The annual evaporation from the trade-wind region of the ocean 

 has been computed, according to the most reliable observation, 

 to be as much as 15 feet, which is at the rate of haK an inch per 

 day. The heat required for this evaporation would raise from the 

 normal temperatm^e of intertropical seas to the boiling-point a 

 layer of water covering the entire ocean to the depth of more than 

 100 feet. Such increase of temperature, by the consequent change 

 which it would produce upon the specific gravity of the sea, would 

 still fm'ther augment its dynamical power, mitil, even in the Atlantic, 

 there would be force enough to put in motion and feed with boiling- 

 hot water many Gulf Streams. But the trade-winds and the seas 

 are so adjusted that this heat, instead of penetrating into the depths 

 of the ocean to raise inordinately the temperature of its waters, is 

 sent ofi" by radiation or taken up by the vapour, or borne away by 

 under currents, or carried off by the winds, and dispensed by the 



p 



